1. Field of the Invention
The present invention relates to a nonvolatile semiconductor memory device, and more particularly to a nonvolatile semiconductor memory device which is used for a NAND flash memory.
2. Description of the Related Art
A NAND flash memory as a nonvolatile semiconductor memory device is developed. Demand for NAND flash memories is rising with an increase in applications using bulk data, e.g., images or moving images in a mobile device or the like. With each generation of NAND flash memory, the memory cell size has shrunk to increase memory capacity.
A memory cell adjacent to a select transistor has a surrounding potential relationship different from that of a memory cell that is not adjacent to a select transistor. Therefore, there is a problem that the characteristics of memory cells fluctuate. To solve this problem, data stored in a memory cell adjacent to a select transistor is reduced to be smaller than data stored in a memory cell which is not adjacent to a select transistor.
However, even though the above-described configuration is adopted, hot electrons caused by a gate-induced drain leakage (GIDL) current produced in source/drain regions of a select transistor at the time of, e.g., a write operation are injected into a memory cell which is adjacent to the select transistor. As a result, there arises a problem that programming error may occur in the memory cell, leading to operation error (see, e.g., “A New Programming Disturbance Phenomenon in NAND Flash Memory by Source/Drain Hot Electrons Generated by GIDL Current” J. D. Lee et al. pp. 31-33 NVSMW 2006).